There are times when sending a pushpage, that a particular ISP will be busy or will be having issues. Our servers (at BBCS) will attempt for a certain period of time to deliver the message. In the event that they cannot deliver in the time limit, it will abort the process and messages like this will pop up.  It just means that the email server (ex. Verizon, AOL, Gmail, etc) wasn't accepting the messages at the time.

Try to resend to the addresses and it's likely they'll send without issue.